It doesn't seem right that tickets could be ignored by support staff and auto-closed as a result. Not sure where your intent was to go with this module, but I'm thinking that auto-close should only happen if someone other than the ticket creator doesn't respond to the ticket. Perhaps that could be an option, but I really hate adding the complexity (for the user, in configuration). For myself, I might get around this behavior by using Change status actions, but since they're not available yet...